Due primarily to consumer preferences, the physical sizes of wireless handheld communication devices continue to shrink while the number of features provided continues to increase. In addition, various wireless devices are now designed to support communications within multiple frequency bands. Each of these developments has impacted the design and performance of antenna systems within contemporary wireless devices.
As is well known, an antenna system of a wireless device provides a means by which radio frequency (RF) power may be radiated into or detected from the environment. Although previous generations of wireless devices commonly included externally protruding antennas, the antennas of many current wireless devices are completely enclosed within a device's housing. Accordingly, an antenna occupies some portion of the physical volume within the device's housing. The continuing drive toward smaller devices places ever-increasing constraints on the amount of space that may be allotted for antenna volumes. In addition, some wireless devices that are designed to support communications within multiple frequency bands include multiple antennas (e.g., one antenna for each supported frequency band), thus increasing the space required for the antenna system, despite the drive toward smaller device sizes. Other wireless devices are designed to support communications using multiple communications protocols on separate frequency bands, again warranting the inclusion of multiple antennas in a single wireless device.
Along with issues relating to antenna volumes, the characteristics of housing-enclosed antenna systems also raise issues relating to performance. More particularly, the performance of an enclosed antenna may be significantly affected by the manner in which a device user holds the wireless device during operation. For example, the compact designs of some wireless devices enable a user to enclose significant portions of the device's housing in the user's hand. In addition, a user may be inclined to press the front surface of the device's housing against the user's face, and accordingly a significant portion of the front surface may be in contact with the user during device operation. The degree of contact between a wireless device and a user's body (e.g., the user's hand and face) may significantly and detrimentally affect the radiation efficiency of the device's antenna (e.g., by perturbing an antenna element's resonant frequency).
More recently, the inclusion of impedance matching circuits in wireless devices has facilitated the development of relatively compact, enclosed antenna systems that may provide reliable communications over multiple frequency bands. Essentially, an impedance matching circuit may be tuned to provide an impedance match for the antenna at a desired operating frequency. Adaptive tuning of the impedance matching circuit in conventional devices is driven by feedback data received from the RF system (e.g., information pertaining to the transmit path and the receive path) and/or information regarding the physical environment around the wireless device. Unfortunately, current systems adapted to provide complete, accurate, and dependable information about the receive path and the physical environment around the wireless device tend to be costly, complex, and difficult to implement.
Accordingly, what are needed are methods and apparatus for tuning an impedance matching circuit, which may be relatively inexpensive, simple, and easy to implement, when compared with conventional methods and apparatus. Other desirable features and characteristics of the present inventive subject matter will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.